An image forming apparatus by means of an electrophotographic method (for example, printer) is provided with a fixing device for heating and melting an unfixed toner image formed on a recording sheet so as to be fixed on the recording sheet. As an example of such a fixing device, an image forming apparatus by means of an electrophotographic method is known for irradiating a toner image with light to heat a toner so as to fix the toner image on a recording sheet without any contact. Such a fixing method is, since a toner is heated without any contact, characterized in that a warm-up is not necessary as compared to a roller fixing method which is a conventional contact heating method.
As such an image forming apparatus for fixing images without any contact by light, for example, Japanese Patent Publication No. 3016685 discloses a fixing device for fixing a toner with use of laser power.
The laser fixing device described in the Japanese Patent Publication No. 3016685 is provided with a plurality of semiconductor lasers and a lens array corresponding to the semiconductor lasers, so that a laser beam emitted from the semiconductor laser is condensed on a recording sheet by the lens array to fix an unfixed toner. This is considered to make it possible to realize a small-sized, inexpensive semiconductor laser fixing device.
The fixing device described in Japanese Patent Publication No. 3016685 controls laser strength by temperature detection means, however, since a toner is heated by a laser in a moment, when a temperature of the toner is detected, heating the toner by the laser has already been finished. Accordingly, it is impossible to control heating in real time while the toner itself is heated. In other words, even if light intensity is controlled by detecting a temperature after the toner is heated in a moment, correct feedback is not able to be performed so that it is impossible to perform appropriate control. That is, a light fixing method is not generally able to perform feedback control of light intensity based on a detection result of a toner temperature.